If the pattern bust is 38 inches, and you need 46 inches, do as Antares said and add extra motifs. It looks like the only shaping is at the neck, the sides seem to be straight up and down.
See how many stitches it states for the 38 inch size, and figure out how many more you need for 8 more inches. Then work the pattern stitch (you may need to add a few extra stitches to make the repeats work put) straight up until you get to the neck shaping, which will not change.
You will probably need to make the armhole openings longer, and the sleeves wider to match, but that will be done in the same way, by adding more stitches to the original directions.